This invention relates to a disc brake and in particular resilient means that aids in moving a caliper with respect to a fixed support bracket after a brake application to establish a running clearance between an outer friction pad and a rotor.
Disc brakes having first and second guide pins that are correspondingly retained in first and second bores in a support member fixed to the frame of a vehicle are known in the prior art. In such disc brakes, the support member receives the spaced apart first and second guide pins to allow the caliper to slide and allow corresponding first and second friction pads to engage with a rotor to effect a brake application. The following U.S. Pat. Nos. 4,448,287; 4,958,703; 4,976,339; 5,526,904; 5,749,445; 5,810,122; 5,810,112; 5,819,884 5,934,416 may be considered typical of such disc brakes. Basically during a brake application, the first and second guide pins slide in the first and second bores as a reaction to a force developed by pressurized fluid being presented to an actuation chamber that acts on an actuation piston to directly move the first friction member toward a rotor. The reaction force is received by the caliper and as a result moves a second friction member toward and into engagement with the rotor during the brake application. On termination the presentation of pressurized fluid to the actuation chamber, the first and second friction members move away from the rotor to establish a running clearance. If either the first or second friction members do not move away from the rotor brake, drag occurs which can cause undesirable wear of both the friction members and rotor. It is known to utilize the resiliency of a seal associated with the actuation piston to assist in the moving the first friction member away from the rotor. Unfortunately, the second friction member is not directly moved away from the rotor but must rely on knock back by the rotor to eliminate brake drag. Brake manufacturers have attempted to reduce brake drag by developing low slide force calipers, however, the components of current disc brakes require tight tolerance to maintain desired operational capabilities. Unfortunately, if such tolerances are not maintained, a perpendicular relationship between the guide pins and rotor is not achieved and caming can occur that causes pin binding that can result in high slide forces. It has been suggested that slide forces could be reduced by increasing the clearance tolerance between the guide pins and bores in the fixed support to provide for a free sliding structure. However, when this type structure was evaluated, noise was created as the pins rattled in the bores when the vehicle traveled on a road having an uneven surface. Rubber insulators that surrounded the guide pins were added to attenuate the noise created by the rattle, unfortunately, this solution reduced the free sliding ability of the caliper and as a result did not completely solve the problem.
A primary object of the present invention is to provide a disc brake having resilient means to assist in defining a running clearance between first and second friction members and a rotor after a brake application.
In more particular detail, the disc brake of this invention has a support member secured to a vehicle with spaced apart first and second bores for receiving corresponding first and second guide pins to position a caliper over a rotor. The caliper has an actuation section located on a first side of the rotor and an arm located on a second side of the rotor. The actuation section has an actuation bore therein for retaining a piston to define an actuation chamber and a bridge connected to an arm. A first friction member is associated with the piston and a second friction member is connected to the arm such that the first and second friction members are positioned on opposite sides of the rotor. The caliper has a first ear that extends from the actuation section for receiving a first head of the first guide pin and a second ear that extends from the actuation section for receiving a second head section of the second guide pin. The relationship between the first guide pin and first bore and second guide pin and second bore is to position the caliper over the rotor such that a parallel alignment is created between the first and second friction members with the rotor. In response to a desired braking of a wheel of the vehicle, the actuation chamber is presented with pressurized fluid from a source. Pressurized fluid, on being presented to the actuation chamber, acts on the piston to develop an actuation force that moves the piston and first friction member toward the rotor while at the same time creating a reaction force which acts on the actuation section and causes the caliper to slide on the first and second guide pins to move the second friction member toward the rotor and effect a brake application. The first and second guide pins are characterized by resilient means that must be overcome by the reaction force before sliding movement of the caliper occurs to effect the brake application and in that the resilient means later acts on the caliper to move the second friction member away from engagement with the rotor to a rest position on termination of the presented pressurized fluid from the source.
An advantage of this disc brake results in a positive caliper retraction on termination of a brake application.
An object of this invention is to provide a disc brake assembly with common and identical leading and trailing guide pins which do not require a bushing on the trailing pin and yet balanced wear for frictions linings is achieved.